THE MERCK MANUAL: The Merck Manual of Diagnosis and Therapymultimedia

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  • Echinococcosis (Hydatid Disease)
  • Echinococcus life cycle.

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    Echinococcus life cycle.

    1. The adult Echinococcus granulosus worm resides in the small intestine of the definitive hosts (dogs, other canines).

    2. Proglottids release eggs, which are passed in the feces.

    3. After ingestion by an intermediate host (usually, sheep, goats, swine, cattle, horses, camels, or humans), the egg hatches in the small intestine and releases an oncosphere, which penetrates the intestinal wall and migrates through the circulatory system into various organs, especially the liver and lungs.

    4. In these organs, the oncosphere develops into a cyst, which enlarges gradually; protoscolices and daughter cysts form within the cyst. The definitive host becomes infected by ingesting the cyst-containing organs of the infected intermediate host.

    5. After ingestion, protoscolices evaginate and attach to the intestinal mucosa.

    6. They develop into adult stages in 32 to 80 days.

    Image from the Centers for Disease Control and Prevention Image Library.

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